Help with setting up a competition process using Squarespace form and coupons

My client sells beer products from their Squarespace website and they want to run a competition. They are running a stand at an upcoming beer and barbeque event next month. Whilst selling beer at the event, they want to encourage people to sign-up to their mailing list by offering new subscribers who have just bought a beer, a free beer when they visit their onsite tap room. In addition, those who sign up at the event, will be entered into a competition to win one of 6 brewery tours.
So far, I think the process could go like this.... 

1) Each time someone buys a beer at the stand, they are asked by staff to scan a QR code. That QR code links to a specially created competition form on an un-linked web page which; 
1) Creates them an account on the website
2) Captures their email, address and phone number 
3) Which then triggers Squarespace to automatically email that new customer account holder a gift card / discounted product / one-use coupon (I'm unsure which to use - any ideas?) for their free tap room beer.

I'm stuck on a few things though…
1) how to automatically make that new customer account holder a part of the competition?
2) How to trigger the one-use coupon or gift card to the account holder and have their name attributed to it (so no one else can use it)
3) how to redeem the gift card / discounted product / one-use coupon in the tap room point of sale

Can anyone please shed some light or better ways to do this?